Sequences in both class ii major histocompatibility complex α and β chains contribute to the binding of the superantigen toxic shock syndrome toxin 1

Class II major histocompatibility complex (MFIC) molecules present peptides derived from processed antigen to antigen-specific CD4-positive T cells. In addition, class II molecules bind with high affinity another class of antigens, termed superantigens. T cell stimulation by superantigens depends almost exclusively on the Vβ segment expressed by the T ceil receptor (TCR). Mapping of the superantigen binding site on class II molecules should provide valuable information on how MHC and TCR molecules interact. Recombinant mouse I-A class II molecules expressed on transfected L cells were analyzed for their ability to bind the toxic shock syndrome toxin 1. Polymorphic residues in the α helices of both the α and β chains of I-A contributed to quantitative toxin binding, suggesting that the toxin binds to either a combinatorial or a conformational site on class II MHC molecules.